In Step 2A, participants will discontinue VPA and will receive intensified therapy (enfuvirtide) administered for 24 weeks twice daily. Study visits will occur at Weeks 25, 28, 32, 36, 40, and 48. A physical exam and blood and urine collection will occur at all visits. Leukapheresis will occur at Weeks 36 and 40. Participants who do not respond to intensified therapy in Step 2A will enroll in Step 3A. Participants who respond to intensified therapy in Step 2A will enroll in Step 3B.